VOL. 8, NO.4
CORRESPONDENCE
729
DEAREDITOR: The criticisms made by Blannl concerning the 32' method of conversion seem to many teachers to be well founded. In teaching elementary physics for many years I have employed as the basis for a very simple rule the two facts, (1) that the relative magnitude of the two kinds of degrees is in the ratio 5/9, and (2) that the number minus 40' expresses the same temperature in both scales. Rule (1) To the given temperature add 40; (2) Multiply this sum by 5/9 or 9/5; (3) From this product subtract 40. The remainder is the desired temperature expressed in the other scale. For those who desire a mathematical formula the relation may he expressed
DEAREDITOR: In connection with the article by Blann' in a recent issue of the JOURNAL OF CHEMICAL EDUCATION, the results of the application of the following plan of temperature conversion to a teaching experiment may he of interest.
Drawing the diagram herewith reproduced as points are mentioned, the pupils fasten first the idea of three points of equivalence on the two scales. Then the degree-distance between these points is called to their attention, and the intervals indicated are reduced to lowest terms, fastening the concept of the 9:5 ratio. This ratio is tried out on a few examples, such as llO°C. being 18'F. more than 212'F.; this also shows the better students how they may use the 1.8 multiplier instead of 9/5 (or also 1.8 as a divisor
' BLANN,J.
CEEM.EDUC., 7, 2946-4 (Dec., 1930).
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JOURNAL OF CHEMICAL EDUCATION
APRIL,1931
instead of multiplying by 5/9). It pays to use a few examples involving negative readings. The rule is simply "add 40, multiply by your fraction, subtract 40" and applies in either direction. With the ratio of g°F. = 5'C. in mind, the proper fraction is easily selected, for the student is made to realize that there are more F. degrees than C. degrees for a given interval. The experiment in teaching was applied to three ability-grouped classes in general science a t West High School, Cleveland. The x, or best group, was two days ahead of the other groups, and was given the old method using the addition or subtraction of 32' on the Fahrenheit side. After two class periods, less than 60% of the class could perform the conversion with consistent accuracy. The third day, about 20 minutes served to bring the entire group to a comprehension of the "minus 40 method," and the performance was almost perfect. They, or average group, was given only the method shown here, with the use of fractions only-not the 1.8decimal. They mastered the situation to a 90% performance within 35 minutes. The lowest group was not strictly z, but managed to attain over 75% performance within a 45-minute period; about ten minutes more spent with the few individuals who needed i t served to bring comprehension to them. At a later date, in two classes in chemistry which were fairly well equated on chemistry performance, the two methods were tried, the "32 method in one group and the "minus 40 method in the other. The resulting tabulation of errors is not a t hand, but was so overwhelmingly in favor of the "minus 40 method that the other has since been discarded entirely. The writer has set up a further analysis of such errors, by a battery of tests now being used in cooperation with the state-wide testing program of the Department of Education of Ohio. The results of analysis of several thousand papers will soon be available. HAROLD WM. BAKER
